Bleaching artificial silk



Patented Jan. 18, 1938 PATENT OFFICE BLEAGHING ARTIFICIAL SILK Homer E. McNutt, Rome, Ga., asslgnor to Tubize Chatillon Corporation No Drawing. Application July 25, 1935, Serial No. 33,064

4 Claims.

This invention is concerned with the prevention of corrosion of aluminum and aluminum alloys during exposure to bleaching solutions, such as solutions of the hypochlorites of alkali metals. More specifically, the invention is concerned with inhibiting the corrosion of aluminum carriers for artificial silk in bleaching operations conducted upon such silks. The invention also contemplates the bleaching of artificial silks in hypochlorite solutions without mercerizing the artificial silk or contaminating it with foreign substances which tend to impair the appearance of the silk, reduce its tensile strength or impair its dyeing properties.

In the manufacture of artificial silk it is cus tomary to bleach the yarn to remove undesirable color bodies from the yarn before it is finally wound on cones, cops, bobbins or into skeins ready for sale. Freshly spun yarn usually is placed on carriers during or soon after spinning. and the amount of labo Qinvolved is reduced if subsequent operations on the yarn (such as bleaching) are conducted while the yarn is' still retained upon these carriers. This is true for artificial silks produced by most of the customary processes, such as the viscose process, the nitrocellulose process and the cupra-ammonium process.

From the foregoing, it will be-clear that it is advantageous to carry on the bleaching operation while the yarn is still held upon the carrier. The bleaching of yarn in loose skeins involves the extra cost of reeling the yarn into skeins and also lowers the yield of first quality yarn due to the tangllng and the tearing of filaments. On the other hand, in the heretofore customary practice, the bleaching of yarn upon carriers has been attendedby difficulty because the hypochlorite bleaching solutions employed are somewhat corroslve and tend to attack the material of which the carrier is made. The salts thus formed frequently have a deleterious effect upon the characteristics of the artificial silk, particularly tensile strength and dyeing properties.

Because of their lightness, strength, and easeof fabrication, aluminum and aluminum alloys are particularly desirable as materials for the construction of carriers, such as bobbins and also for containers such as tanks, pipes and valves. However, the use of such aluminum carriers has been restricted by the fact that the customary bleaching solutions, such as solutions of sodium hypochlorite or potassium hypochlorite, usually contain considerable free alkali. This 'free alkali attacks the aluminum, and produces aluminum rites.

salts which impregnate the artificial silk. The impregnation of artificial silk with salts of aluminum results in a marked deterioration of the tensile strength and dyeing properties of the artificial silk. Aluminum salts alsoaffect the appearance of the silk deleteriously. For this 1 reason, when hypochlorite solutions are employed it has been necessary to bleach the yarn in skein form out of contact with aluminum. Another alternative in the heretofore customary art has been to use other and less efl'ective bleaching agents which do not corrode aluminum carriers.

Throughout the specification, and claims I use the term aluminum to include both pure aluminum and aluminum alloys. I

The commercial sodium hypochlorite which is used for making up bleaching solutions for artificial silk usually contains free'alkali in the form of sodium hydroxide or sodium carbonate. The presence of free alkali increases the stability of 20 the material, and permits it to' be stored for long periods prior to use. At the same time these free alkalis tend to corrode aluminum and to partially mercerize the artificial silk during the bleaching operation. 25

As a result ofmy investigations, I have discovered that it is possible to inhibitthe corrosion of aluminum carriers and containers and at the same time prevent partial mercerization by neutralizing the free alkali in alkali metal hypochlo- 30 rite bleaching solutions with weak acids and acid salts of weak acids. These weak acids should be of such character as not to affect the artificial silk itself, or toform compounds which are deleterious to the artificial silk. Furthermore, the weak acid or weak acid salt should be substantially non-reactive with alkali metal hypochlo- Otherwise, a high loss of reagent occurs. Among the weak acids which may be employed are carbonic acid, acetic acid, boric acid, and mixtures of these weak acids. Certain acid salts may also be employed. Borax, for example, considered'as sodium acid borate may be used. I prefer to use bor'ax or boric acid, but other weak acids or weak acid salts'may be employed provided that they do not react with the hypochlorite and do not affect the artificial silk deleteriously. V

In neutralizing the free alkali in the bleaching solution (for example, sodium hypochlorite so-' lution) I prefer to add just enough of the weak acid or weak acid salt to neutralize all of the free sodium hydroxide and one half of the sodium carbonate, thus converting the free sodium hydroxide to sodium bicarbonate and to the sodium salt of the weak acid employed.

My invention is applicable to bleaching solutions of high and low concentrations, but I prefer to use a solution having concentrations less than 0.5% available chlorine. The free alkali content of the sodium hypochlorite or other bleach solution may vary without affecting the results, provided that the free alkali is neutralized with an appropriate weak acid or 'weak acid salt. In practice, -I have obtained exceedingly satisfactory results by using a sodium hypochlorite bleach solution which contained 0.15% available chlorine and a free alkali content of .04% calculated as sodium hydroxide. The tree alkali content of the solution was neutralized with a molecular equivalent of boric acid before use.

The temperature of the treatment may vary. but satisfactory results have been obtained by using the neutralized bleaching solutions at room temperature. In order to obtain a uniform degree of bleaching, it is desirable that the temperature of the bleached solution be maintained constant.

My invention may be more thoroughly understood in the light of the following example: I

Freshly spun viscose artificial silk was first washed to free it of excess coagulant and then desulphurized on aluminum bobbins. The excess desulphurizing solution 'was washed out of the artificial silk and the aluminum bobbins containing the desulphurized silk were immediately immersed in a bleaching solution containing .12% of available chlorine. The original free alkali content 01' this bleached solution was 414%, but this had been entirely neutralized by the addition of .a very slight excess borax; The bleaching solution, at a temperature of 25 C. was forced continuously through the artificial silk on the bobbins for a period of two hours. The silk was then withdrawn and washed to tree it from excess bleach solution.

Yarn treated as set forth in the above example may be simiected to any finishing operation such :1 (leiilbrication, sizing, dyeing, tinting and finally Artificial silk treated in accordance with my invention is superior in tensile strength and dyeing properties to artificial silk which has been bleached with an alkali metal hypochlorite-in the presence of free alkali. Artificial silk produced amassc in accordance with my invention is also superior in appearance, and is substantially free of aluminum salts.

My invention is applicable to the bleaching of artificial cellulose filaments or natural cellulose fllaments. For example, it may be employed advantageously in the bleaching of regenerated cellulose produced by the viscose, nitrocellulose, and/or cupra-ammonium processes, and natural cellulose such as cotton, jute, ramie, or flax.

I claim:

1. A method for inhibiting the corrosion of aluminum in the presence of an aqueous solution containing an alkali metal hypochlorite and free alkali which comprises neutralizing the free alkali content of the solution with'a compound selected from the groupconsisting of carbonic acid, acetic acid, boric acid and borax, and bringing the solution thus neutralized into contact with the aluminum.

2. In the bleaching of artificial silk on aluminum carriers with an aqueous solution of so dium hypochlorite containing tree alkali, the improvement which comprises neutralizing the free alkali in the solution with borax and bringing the solution thus neutralized into contact with the artificial silk on the aluminum carriers, thereby inhibiting the corrosion of the aluminum and preventing the contamination of the artificialsilk with aluminum salts.

3. A method of bleaching artificial threads of regenerated cellulose disposed on aluminum carriers which comprises neutralizing the free. sodium hydroxide and sodium carbonate content of an aqueous sodium hypochlorite solution with a compound selected from the group consisting of carbonic acid, acetic acid, boric acid and borax, and bringing the artificial threads disposed on the'aluminum'carriers into contact with the solution thus neutralized.

4. In a method of producing artificial silk the step of bleaching the artificial silk disposed on aluminum carriers which comprises subjecting said silk and carriers to a hypochlorite bleaching solution containing a sufllcient quantity of a compound selected from the group consisting of carbonic acid, acetic acid, borlc acid and borax to inhibit the corrosion of the carriers by the hypochlorite.

Y HOMER E. McNU'I'I. 

